Meters used on motorcycles include digital displays of, for example, running time, engine temperature and other information. Since the motorcycles may be of the trail-type for traversing rough terrain, the meters must be robust to withstand vibration and shock. The meters must also be well sealed to prevent penetration of fine dust and moisture into the meter. For convenience, the interior of the meter housing that includes the electronic and other components and that is intended to be protected from penetration of dust and moisture will be referred to as the meter compartment, or simply “compartment.”
In the past, the technique for sealing the meter compartment included a small, passive vent that enabled filtered air to pass into and out of compartment. Thus, the pathway between the compartment and ambient air is continuously open, and the filter is relied upon for preventing penetration of fine particles. The continuously open air pathway compensates for changes in ambient pressure by permitting air flow between the compartment to equalize pressure inside and outside of the meter. In such a design, it is important that the vent also prevents the passage of moisture into the compartment while allowing the pressure-equalizing air flow. To this end, porous hydrophobic material is often selected for use as vent's filter, which spans an opening or passage into the compartment. Such material is not, however, completely effective, and over time the continuously open venting approach will enable moisture to accumulate within the meter compartment, which leads to corrosion and other problems, including fogging of the meter display when the moisture condenses on it.
One prior solution to the forgoing problem is to place a package of desiccant material within the compartment, but this merely delays the problem for as long as it takes for the desiccant to saturate.
Completely sealing the compartment (that is, eliminating the continuously open vent) is not a practical option because large changes in ambient pressure, such as pressure drops occurring when meters are shipped by air or otherwise transported to high-elevations, can lead to failure of the compartment water seals and/or distortion of the display and other components.
The present invention is directed to a solution to the forgoing problem and provides, among other things, a way of compensating for the pressure changes affecting sealed compartments by eliminating the prior art, continuously open pathway between ambient air and the compartment interior, while occasionally and briefly opening the pathway to prevent damage from extreme pressure differences.
Other advantages and features of the present invention will become clear upon study of the following portion of this specification and drawings.